Overhead protection system

ABSTRACT

A protective shelter is disclosed. The shelter may be sized to protect an existing, unhardened structure, and its contents. Or, the shelter may be sized to protect an individual or other objects of similar size. In either case, the shelter provides protection from blasts from explosive shells, rockets, and the like. The shelter has a support frame that supports a blast cover that is positioned above the object or objects to be protected. A burster screen is positioned above the blast cover and may be supported by the support frame. The burster screen serves to detonate incoming ordinance before the ordinance reaches the protected object or objects. The blast cover is strong enough to withstand the resulting shock from the detonated ordinance, and thus prevents damage to the protected object or objects located below the protective shelter. This invention may be used to retrofit existing, unhardened structures in areas where additional protection is needed. It also may be used as part of the design of new facilities, and offers the option to later remove the hardened, protective part of the structure if the threat level changes for the better. In the smaller, personnel-protection embodiment, the invention may be air dropped to remote locations and assembled by personnel in the field.

FIELD OF THE INVENTION

The invention relates to a protective structure, and in particular to a protective structure built to protect another structure or personnel from harm caused by blasts resulting from explosive shells, rockets, and the like.

BACKGROUND AND SUMMARY OF THE INVENTION

Terrorism, war, and other hostile situations are regrettably common around the world. The nature of the threat level often changes, making it difficult to have the proper type of protective structures in place at all locations. For example, military facilities in some locations are built with a relatively low level of hardening because the threat level in the area was not particularly high when the facilities were constructed, or for other reasons. In some instances, facilities originally built by one government or force are taken over by another, and the facilities may not have sufficient protection given the new threat levels faced.

When this happens, the government or other entity operating the facilities must make difficult decisions. It can withdraw key forces from the location to reduce their exposure to threat. That, however, may leave the force unable to respond to the threat in an effective manner. Alternatively, the government or entity may build new facilities that are hardened against incoming blasts to replace the existing unhardened facilities. That is a very expensive and time-consuming approach, but it does yield good results in terms of protecting the force and keeping the force where it needs to be.

An example of the situation described might be a military installation with small to mid-sized aircraft hangers, perhaps hangers for helicopters. If these hangers were not built to withstand the blast of incoming ordinance, they will be at risk if the threat situation changes such that incoming ordinance is a real threat. This is a fairly common situation as more small militia and terrorist groups obtain the firepower to launch offensive attacks on military installations around the world. Even a relatively small militant group may now be able to launch small surface-to-surface missiles at a military facility. Such a missile could pose a serious threat to an unhardened aircraft hanger like those mentioned above.

Something must be done to protect existing, unhardened structures from such damage, and to protect the equipment and personnel within those unhardened structures. The option of constructing entirely new buildings (e.g., new, hardened aircraft hangers) may be too expensive and typically takes a long time to accomplish. Some alternative is needed.

The present invention provides the needed alternative. A protective structure designed to be built around an existing, unhardened structure is disclosed. This retrofit approach is cost-effective, easy to build, and relatively quick to construct. It does not require any change to the existing structure, and in many cases, will allow operation and use of the existing structure to continue without interruption during construction. This latter benefit is important, particularly if the facility being retrofitted is involved in active operations against an enemy threat.

The invention has a support frame that is built outside the existing structure. A blast cover, made of pre-formed concrete panels in a preferred embodiment, is supported by the support frame. The invention is limited in size because the blast cover is heavy and requires substantial support. If the structure is too wide, it is difficult to provide the needed support using only a frame constructed around the existing structure. The present invention works well for situations requiring up to a 20 meter wide support frame, and will work for any length structure.

Once the support frame and blast cover have been constructed, a burster screen is installed an appropriate distance above the blast cover. The burster screen is made of thin, light material. Its function is to create enough resistance to incoming ordinance to cause the ordinance to detonate. By positioning the burster screen away from the blast cover, the incoming ordinance will explode above the blast cover rather than on it. This greatly reduces the destructive force of the ordinance, and allows a relatively modest blast cover to provide adequate protection against most types of ordinance. The burster screens serves to trigger the explosives a fixed distance away from the blast cover.

If a protective structure built in accordance with the present invention comes under attack, the burster screen will be destroyed or heavily damaged. It is intended to be a replacement structure. If a sufficiently large explosion occurs, it is quite possible that some or all of the blast cover might also be damaged and require repair or replacement. Even when that happens, however, the existing, unhardened structure has been protected, and a relatively inexpensive and quick repair will leave the structure protected again. In this sense, the present invention is something of a sacrificial structure, at least in part, designed to fail in order to prevent failure of the protected structure.

There is a further, and related, need for blast protective structures that are small enough to be air lifted to remote locations. Such structures should be easy to assemble by field personnel. The structures should provide protection to personnel from blasts, in the manner summarized above. The present invention meets these needs, too, by providing a smaller version of the blast protection structure. This smaller version is ideally suited to protect individual soldiers or others in harms way.

In a preferred embodiment, the present invention is protective shelter having a support frame positioned exterior to a protected object; a blast cover positioned above the protected object and supported by the support frame; and a burster screen supported by the support frame and positioned a safe blast dissipation distance above the blast cover. Alternatively, the invention embodies a method of constructing a protective bunker, with the steps of constructing a rigid support frame using pre-cut and pre-drilled beams; constructing a blast cover by stacking one or more layers of blocks around the rigid support frame; and, covering the rigid support frame and blast cover with at least one foot of locally obtained fill material. Further embodiments and details are provided in the detailed description below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the present invention.

FIG. 2 is a front-view of a preferred embodiment of the present invention.

FIG. 3 is a side-view of a preferred embodiment of the present invention.

FIG. 4 is a perspective view of a preferred embodiment of the present invention.

FIG. 5 is a cut-away top view of a burster screen of a preferred embodiment of the present invention.

FIG. 6 is a front-view of a smaller, personal-protection version of the present invention.

FIG. 7 is a top-view of a smaller, personal-protection version of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Turning to the figures, the present invention can be best understood by starting with a functional diagram. In FIG. 1, a block diagram illustrates the basic structure and purpose of the present invention. A protective structure 10 is shown built around an existing, unhardened structure 12. A lower support frame 14 is shown supporting a blast cover 16 and burster screen 18. Incoming ordinance 20 is shown just making contact with the burster screen 18. This contact causes the ordinance 20 to detonate.

The burster screen 18 is positioned about 1-3 meters above the blast cover 16 in a preferred embodiment. The shrapnel, blast wave, and heat created by the detonation of the ordinance 20 dissipates somewhat before making contact with the blast cover 16. These destructive forces are deflected and absorbed by the blast cover 16, and the existing, unhardened structure 12, is thus protected from the incoming ordinance. The particular structural components of the preferred embodiment of the invention are described in more detail below.

The burster screen 18 may be made of any material with sufficient rigidity to detonate incoming ordinance. The needed separation between the burster screen 18 and the blast cover 16 will vary depending upon the type of ordinance expected, the size and strength of the blast cover, and possibly the hardness of the structure being protected. The required distance between the burster screen 18 and the blast cover 16 can be defined as a safe blast dissipation distance, which is the amount of distance required to ensure that incoming ordinance do not compromise the structure or object being protected by the shelter. The safe blast dissipation distance will vary somewhat, but typically will be at least one meter, and rarely will exceed three meters. For the bunker embodiment of the invention discussed below in connection with FIGS. 6 and 7, the safe blast dissipation distance may be as little as one foot.

FIG. 2 is a front view of a preferred embodiment of the protective structure 10. The existing, unhardened structure 12 in this illustration is a small aircraft hanger. A helicopter hanger is shown here, with a protected helicopter 22 inside. A typical unhardened helicopter hanger may be about 16 meters in width. The protective structure 10 would be constructed outside the unhardened hanger. A distance of less than one meter between the outer wall of the hanger and the inner side of the protective structure 10 is sufficient to allow workers to build the protective structure. It is desirable to minimize the space between the existing structure 12 and the new protective structure 10 in order to avoid wasting space, and because the shorter the distance between the two sides of the lower support frame 14, the stronger that frame will be.

The blast cover 16 is shown just above the top of the existing hanger 12 in FIG. 2. Some separation is desirable here to allow for some movement of the blast cover 16 without causing damage to the existing structure 12. Less than a meter is needed for this purpose. The blast cover 16 is supported by the lower support frame 14. As this drawing shows, the lower support frame 14 must support the entire weight of the blast cover 16, the burster screen 18, and any additional support materials. In addition, the lower support frame 14 may need to provide such support entirely from along the sides of the existing structure 12. In many situation, both the front and back of the existing structure 12 will require full, unrestricted access, a fact that prevents extending the lower support frame 14 all the way around the existing structure 12. In other situations, however, it may be possible, and desirable, to extend the lower support frame 14 partially around one or both ends of the existing structure 12.

The burster screen 18 is shown supported by an upper support frame 24 in FIG. 2. This upper support frame 24 may be built on top of the blast cover 16. In a preferred embodiment, the upper support frame 24 is also attached to the lower support frame 14. The upper support frame 24 may be of relatively light weight materials because the burster screen 18 need not have a great deal of structural strength, as is explained below.

FIG. 3 is a side view of the embodiment shown in FIG. 2. The existing structure 12 is seen through the lower support frame 14. The outsides of the protective structure 10 of this invention are open, as there is no need to enclose the sides of the structure. Siding could be installed if there is a reason to hide the entire protected structure 12, but such siding is not necessary for the protection provided by the present invention.

The lower support frame 14 is shown with optional cross supports 26. These supports enhance the rigidity and strength of the lower support frame 14. The blast cover 16, upper support frame 24, and burster screen 18 are also shown in FIG. 3.

FIG. 4 is a perspective view showing more detail of the blast cover 16. In the embodiment shown, the blast cover 16 is supported by blast cover cross braces 30 and longitudinal braces 32. Blast cover slabs 34 are placed on this supporting structure. The blast cover slabs 34 may be pre-formed, which may simplify and speed up the process of constructing the protective structure 10. Alternatively, the blast cover 16 may be formed on site, using a solid lower frame into which liquid concrete is poured. This alternative is not illustrated, but is a common construction method. Upper floors in multi-story buildings are often formed by using a solid concrete formwork into which liquid concrete is pumped. The same, or a similar, process can be used to form the blast cover 16 of the present invention.

The pre-formed slabs 34 are preferred, however, because they may make construction easier and it eliminates the need for a full lower structure for the blast cover 16. The pre-formed slabs 34 used in this preferred embodiment are somewhat similar to the slabs used to construct bridges and other road structures. The slabs 34 may be up to about 20 cm in thickness and made of concrete. When a protective structure 10 is made in the manner show in FIGS. 2-4, a width of up to about 20 meters is possible. Greater widths may be possible by either using a lighter and/or thinner blast cover 16, or by enhancing the size and strength of the lower support frame 14. The vertical posts of the lower support frame have foundations 28. These are positioned about 6 meters apart in a preferred embodiment. The support frame members may be made of hot-rolled structural steel.

FIG. 5 shows a cut-away of part of a burster screen 18. In this embodiment, a burster screen frame 40 is constructed on the upper support frame 24. Thin, metal panels 42 and then installed on the burster screen frame 40. This construction is similar to that used for metal buildings and standing seam metal roofs, and is well-known in the construction field. U.S. patent application Ser. No. 11/906,455 discloses a security fence using a simple to construct metal frame and metal panels. This application is hereby incorporated by reference into the present application. The burster screen 18 of the present invention may be constructed in a somewhat similar manner to the frame and panel parts of the security fence disclosed in the referenced application.

The burster screen 18 is positioned about 1-3 meters (about 3-10 feet) above the blast cover 16. The burster screen 18 is sufficiently strong and rigid to trigger a contact fuse on incoming ordinance. This causes the ordinance to detonate when it strikes the burster screen 18, rather than the blast cover 16. A good part of the explosive energy of the ordinance is thus dissipated in the air before making contact with the blast cover 16. This key feature of the present invention allows the use of sufficiently light materials for the blast cover to allow for a retrofitted structure that will cover many existing unhardened structures. If larger charges are expected, the burster screen 18 can be positioned farther above the blast cover 16, thus allowing for more of the force to dissipate.

The present invention will not protect all existing unhardened structures and it will not protect against all threats. Some buildings are simply too large, and some threats are simply too destructive. In addition, some threats are not delivered through the air. For example, a suicide bomber may enter a facility and detonate a charge. The present invention is not designed to protect against that type of threat. It is expected, however, that the present invention can protect 90% or more of existing unhardened structures from about 90% of the incoming ordinance threats. The present invention offers a cost-effective means of retrofitting many structures in harm's way.

The present invention also may be used with new construction. A new facility may be built in the normal manner, without additional hardening. The present invention may then be built around the new facility. The simplicity of the present invention may allow the protective structure 10 to be completed even before the interior of the protected structure is completed. This approach may be just as cost-effective as adding hardening features to the design of the new facility, and also might allow for removal of the protective structure if the situation changes and such protection is no longer needed.

The method of protecting an unhardened structure, therefore, is applicable in almost any situation. It does not require much additional space, is easy to construct, and is cost-effective. This process offers many advantages over retrofitting in the traditional manner.

The present invention is also quite versatile. It can be used in a scaled-down version to protect personnel (e.g., soldiers) in the field. Soldiers traditionally have used fox holes or dug out trenches for protection from incoming blasts. In some areas, it is not practical to use this type of protection, and even where possible, these traditional techniques do not provide enough protection from overhead blasts or falling objects. The present invention can be used to provide an alternate personnel protection structure.

FIG. 6 shows a front view of a preferred embodiment of a personal bunker 50 constructed according to the present invention. The bunker 50 has some of the same key components described above, though in a somewhat different form. The structural support frame 52 in FIG. 6 provides support for the blast cover 54. These two parts of the bunker 50 serve the same purpose as the support frame 14 and blast cover 16 shown in FIGS. 1-4, and described above. In the personal bunker embodiment of the invention, the structural frame 52 may be made of steel beams (“I” type beams are an acceptable type) pre-cut and pre-drilled for easy assembly in the field. The blast cover 54 is made of bricks, concrete blocks, or some other similarly dense, but relatively small items that fit together to form a tight, nearly-solid, cover.

The embodiment shown in FIG. 6 uses two layers of concrete blocks for the blast cover 54. This provides a reasonable degree of protection from blasts. Precast, interlocking concrete blocks are a preferred material for the blast cover 54. Once the structural frame 52 is assembled, the blocks are placed on the frame, forming the blast cover 54. In a preferred embodiment, an impermeable membrane 56 is then placed over the blast cover 54. This membrane 56 prevents moisture and debris from entering the bunker 50 through the blast cover 54.

In place of the burster screen shown in FIGS. 1-5, a mass fill 60 may be used in the personal bunker embodiment. Alternatively, a thin, sheet metal burster screen, similar to that described above, may be used. The support frame 52 may be constructed with an upper support, upon which an upper burster screen may be constructed. Other materials also may be used for the burster screen in this embodiment, including a wood frame or even a hard plastic or polyethelene-type material. The primary requirement for the burster screen is the same as was described above: the screen should capable of detonating incoming ordinance a sufficient distance from the blast cover to allow much of the damaging force to dissipate.

In the personal bunker embodiment, it is convenient to use a mass fill 60 as a burster screen. The outer surface of the mass fill provides a contact surface capable of detonating incoming ordinance. By using a sufficient thickness of locally obtained fill material (e.g., earth, sod, etc.) placed over the impermeable membrane 56, the mass fill 60 becomes a burster screen, while also providing additional protection. If used, the mass fill 60 should be at least one foot thick, and preferably is about two feet thick. The outer surface of the mass fill 60 serves as a burster screen, in much the same way as the screen described above. In addition, the mass fill 60 provides additional blast protection because the fill 60 typically will be a relatively solid material. It is important to use a reasonably thick mass fill 60 so that the blast of an incoming round will burst some distance away from the primary blast cover 54. This separation of the actual blast from the blast cover 54 remains a key feature of the present invention. If a separate burster screen is used (e.g., of wood, sheet metal, or other material), it is preferable to locate the screen about one meter above the blast cover.

To help hold a thick layer of mass fill 60 in place, boxed supports or anchoring material 68 may be placed at the base of each side of the bunker 50. For example, Hesco-type structures, filled with local material, may be placed a few inches away from the bottom edges of the blocks that make up the blast cover 54. The mass fill 60 may then be placed over the entire bunker 50, with the anchoring material 68 helping to hold the mass fill 60 in place, and allowing use of a thicker layer of fill 60.

The structural frame 52 is preferably bolted together in the field. It can be anchored in place using anchor pins 62, and anchoring stones 64 or other anchoring objects. The two base ends of the frame 52 may be connected using a cross brace line 66. In a preferred embodiment, the cross brace line 66 is a wire rope that is connected at its ends with clevis plates and pins. A turn buckle may be used to tighten the wire rope. The cross brace line 66 helps hold the structural frame 52 in place and helps prevent flattening of the bunker 50 by an incoming blast.

FIG. 7 shows a top view of the personal bunker embodiment of the present invention. The cut-away nature of FIG. 7 allows presentation of the structural frame 52 and the blast cover 54. This view gives a better sense of how the bunker 50 is constructed.

The key components of the personal bunker embodiment may be air lifted to remote locations and dropped to soldiers in the field. The structural frame components, the blast cover blocks, and the anchoring hardware are all that are needed for construction of the bunker 50. Other materials are locally sourced. Using the present invention, field personnel are able to construct safe, secure personal bunkers in relatively little time. These bunkers are stable, will last as long as needed, and provide better protection than more traditional alternatives.

While the preceding description is intended to provide an understanding of the present invention, it is to be understood that the present invention is not limited to the disclosed embodiments. To the contrary, the present invention is intended to cover modifications and variations on the structure and methods described above and all other equivalent arrangements that are within the scope and spirit of the following claims. 

1. A protective shelter comprising: a. a support frame positioned exterior to a protected object; b. a blast cover positioned above the protected object and supported by the support frame; and c. a burster screen supported by the support frame and positioned a safe blast dissipation distance above the blast cover.
 2. The shelter of claim 1, wherein the burster screen is constructed of a light-weight material.
 3. The shelter of claim 2, wherein the burster screen is constructed of thin, sheet metal.
 4. The shelter of claim 1, wherein the safe blast dissipation distance is at least one meter.
 5. The shelter of claim 1, wherein the blast cover is constructed of concrete.
 6. The shelter of claim 1, wherein the support frame further comprises a lower support frame that provides structural support for the blast cover, and an upper support frame that is supported by the lower support frame and provides structural support for the burster screen.
 7. The shelter of claim 1, wherein the protected object is an existing, unhardened structure.
 8. A protective shelter constructed around an existing structure, the protective shelter comprising: a. a burster screen; b. a blast cover positioned a safe blast dissipation distance below the burster screen; c. an upper support frame connected to the burster screen and the blast cover, and supporting the weight of the burster screen; and, d. a lower support frame built around the exterior of the existing structure and configured to support the weight of the burster screen, the blast cover, and the upper support frame without placing any structural demands upon the existing structure.
 9. The shelter of claim 8, wherein the blast dissipation distance is at least one meter.
 10. The shelter of claim 8, wherein the burster screen is constructed of thin, sheet metal.
 11. The shelter of claim 10, wherein the burster screen is positioned between approximately one and three meters above the blast cover.
 12. The shelter of claim 11, wherein the blast cover is constructed of concrete.
 13. A protective bunker comprising: a. a structural frame; b. a blast cover supported by and positioned around the structural frame; and, c. a mass fill supported by the structural frame and positioned around the blast cover, wherein the mass fill is of sufficient thickness to cause an incoming explosive device to detonate at a safe distance from the blast cover and structural frame.
 14. The bunker of claim 13, wherein the structural frame further comprises pre-cut and pre-drilled steel beams configured for field construction.
 15. The bunker of claim 13, wherein the blast cover further comprises at least two layers of blocks.
 16. The bunker of claim 13, wherein the blast cover further comprises precast, interlocking, concrete blocks.
 17. The bunker of claim 13, wherein the mass fill is at least one foot thick.
 18. The bunker of claim 14, wherein all components except the mass fill are pre-packaged into a field-ready kit that may be delivered to a field location for assembly.
 19. A method of constructing a protective bunker, comprising: a. constructing a rigid support frame using pre-cut and pre-drilled beams; b. constructing a blast cover by stacking one or more layers of blocks around the rigid support frame; and, c. covering the rigid support frame and blast cover with at least one foot of locally obtained fill material.
 20. The method of claim 19, further comprising air-dropping all components except the locally obtained fill material to a field location for assembly. 